Method and system for controlling partial pressure of air in an intake manifold of an engine

Abstract

A method for controlling partial air pressure in an intake manifold of an engine. The engine has an intake throttle device for controlling a flow of air to the intake manifold. An EGR valve is provided for controlling a flow of exhaust gas from the engine to the intake manifold downstream of the intake throttle. The engine has at least one cylinder fed a flow comprising air passing through the throttle to the intake manifold and exhaust products passing through the EGR valve to the intake manifold. Both the air through the throttle and the exhaust gas products in the intake manifold are passed as a combined flow to the intake manifold and then to the at least one cylinder. The method includes: specifying a dynamic reference model for the desired partial pressure of the air as a function of time; and controlling the flow through the intake throttle device in accordance with an estimated EGR flow obtained by a dynamic observer and an estimate of partial air fraction in the exhaust gas products. In one embodiment, the partial air fraction is estimated in accordance with intake to exhaust delay and fuel injection to exhaust delay. In one embodiment the dynamic observer does not require information of engine exhaust temperature, engine exhaust pressure, or EGR valve position.

What is claimed is:  
     
       1. A method for determining partial air pressure in an intake manifold of an engine, such engine having an intake throttle device for controlling a flow of air to the intake manifold, an EGR valve for controlling a flow of exhaust gas from the engine to the intake manifold downstream of the intake throttle, at least one cylinder fed a flow comprising air passing through the throttle to the intake manifold and exhaust products passing through the EGR valve to the intake manifold, both the air through the throttle and the exhaust gas products in the intake manifold passing as a combined flow to the intake manifold and then to the at least one cylinder, such method comprising: 
       estimating the flow of exhaust gas products passing through the EGR valve to the intake manifold;  
       determining intake manifold pressure;  
       determining air flow through the throttle device to the intake manifold;  
       estimating the air fraction in the portion of the exhaust gas products passing to the intake manifold;  
       combining the estimated flow of gas products, the determined intake manifold pressure, with the estimated air fraction to determine the partial air pressure in the intake manifold.  
     
     
       2. The method recited in  claim 1  wherein the estimate of the air fraction comprises using an open loop estimator. 
     
     
       3. The method recited in  claim 1  wherein the estimate of the flow of gas products passing through the EGR valve comprises providing such estimate in accordance with an open loop estimator. 
     
     
       4. The method recited in  claim 3  wherein a dynamic observer is void of information of engine exhaust temperature. 
     
     
       5. The method recited in  claim 3  wherein a dynamic observer is void of information of engine exhaust pressure. 
     
     
       6. A method for controlling partial air pressure in an intake manifold of an engine, such engine having an intake throttle device for controlling a flow of air to the intake manifold, an EGR valve for controlling a flow of exhaust gas from the engine to the intake manifold downstream of the intake throttle, and, at least one cylinder fed a flow comprising air passing through the throttle to the intake manifold and exhaust gas in the intake manifold passing through the EGR valve to the at least one cylinder, such method comprising: 
       estimating partial air pressure in intake manifold based on open loop observer and estimated partial air fraction in the flow of exhaust to the intake manifold.  
     
     
       7. An engine control unit programmed to execute the following: 
       estimate partial air pressure in an intake manifold based on open loop observer and estimated partial air fraction in a flow of exhaust to the intake manifold.